The present invention relates generally to integrated circuit device mounting assemblies and, more particularly, to an apparatus for implementing a self-centering land grid array (LGA) socket.
Area array socket connectors are an evolving technology in which an electrical interconnection between mating surfaces is provided through a conductive interposer. One significant application of this technology is the socketing of land grid array (LGA) modules directly to a printed wiring board, in which the electrical connection is achieved by aligning the contact array of the two mating surfaces and the interposer, then mechanically compressing the interposer. LGA socket assemblies are prevalent today in the electronics industry, and are commonly used to attach both single chip modules (SCMs) and multi-chip modules (MCMs) to printed wiring boards.
Integrated circuits, such as those mounted in LGA assemblies for example, are commonly tested before installation. Accordingly, test sockets are primarily used to determine whether the integrated circuit functions properly, and can make the required electrical connections to pads or leads on the integrated circuit package. In a test system, the test socket is typically mounted on a test circuit board coupled to a control unit. The test circuit board typically includes electronic interconnects (e.g., thin, narrow conductive strips) for coupling electronic signals between the test socket and a control unit. The control unit, in turn, includes a processor that communicates with a device under test (e.g., a packaged electronic circuit mounted on the test socket) by transmitting electronic signals to the packaged electronic circuit and receiving electronic signals from the packaged electronic circuit.
With such testing, there is a need for repeated, accurate centering of LGA substrates within test sockets. Moreover, the test socket should be able to accommodate variations of ±8 mils or more in substrate size, and must also be easy to load and unload in a manufacturing environment. Currently, conventional sockets (including test sockets) incorporate plastic spring fingers in the support frame thereof. Unfortunately, however, there are several disadvantages associated with the present spring finger design. For example, even where a substrate is properly seated in the socket, there is typically poor tactile feedback for indicating a proper insertion. Furthermore, the insertion of a substrate within a socket can generate plastic debris that contaminates the socket.
Still another consideration is the difficulty associated with loading and unloading substrates; if a substrate is misloaded, one or more spring fingers may easily be sheared off, thereby destroying the socket (since spring fingers cannot be repaired or replaced). Even if not destroyed, the spring fingers are still subject to conditions such as wearing, shaving, and thermal fatigue/stress (due to operating temperatures at about 100° C.). In any case, it is also difficult to balance and adjust the spring rates of machined or molded plastic fingers, which are further subject to spring rate variations caused by material anisotropy. Due to the high friction of spring fingers against a substrate edge, a poor centering capability also results.
In view of the above, it would be desirable to overcome the above described shortcomings by configuring a self-centering LGA socket that (among other aspects) provides ease with respect to loading and unloading substrates (i.e., has low friction), as well as good tactile feedback when the substrate is properly seated therein.